Sequential Acid–Cyanide Diagnostic Leaching to Quantify Cyanide-Soluble Copper in a Gold-Bearing Oxidized Copper Ore

Copper-bearing minerals can strongly interfere with gold cyanidation because dissolved copper forms stable Cu(I)–cyanide complexes and competes for free cyanide. This study applies sequential acid–cyanide diagnostic leaching to four oxidized copper ore samples from a gold-bearing ore population to quantify cyanide-soluble Cu and determine whether sulfuric acid pre-cleaning materially suppresses that burden. Head Cu concentrations ranged from 0.659 to 1.355 wt.%. A triplicate head-Au determination on PQ-CU010 gave 0.66, 0.56, and 0.57 g/t, corresponding to 0.597 ± 0.055 g/t Au. PQ-CU010 was considered representative of the same ore population as PQ-CU011–PQ-CU013; therefore, this mean was adopted as the representative head-Au value for the investigated sample set, while Au was not independently determined in the other three samples. A 48 h sulfuric-acid diagnostic treatment removed 40.54–78.93% of head Cu, equivalent to 5.18–6.31 kg Cu/t ore. Direct cyanide diagnostic tests dissolved 0.673–1.179 kg Cu/t, corresponding to 5.57–17.88% of head Cu. After acid pre-cleaning, the cyanide-soluble Cu load decreased to 0.244–0.616 kg/t on an original-ore basis, representing suppression of 26.8–79.3%. Mineralogical analysis assigned 76.5–93.8% of Cu to biotite-associated populations, 5.3–23.5% to Mn-oxide-associated populations, and 0–3.2% to Cu oxy-hydroxides. The response was strongly sample-specific: PQ-CU010 showed the greatest suppression of cyanide-soluble Cu, whereas PQ-CU013 retained a comparatively high post-acid burden despite substantial acid-soluble Cu removal. Because paired gold-extraction and actual NaCN-consumption tests were not included in the analyzed dataset, the study supports pretreatment selection on a diagnostic basis but does not establish plant-scale reagent savings, gold-recovery improvements, or an economic optimum. Direct and sequential cyanide-soluble Cu measurements provide a more defensible process-selection criterion than bulk Cu grade alone.